Sun shades are commonly used to shade outdoor living areas such as sun decks. In many climates prolonged exposure to the sun is dangerous, and often the usability of an outdoor living area can be enhanced by shading the area from direct sunlight.
However there are times when a sun shade is not desirable, for example where the warmth or tanning effects of the sun are desired, or at night when a sun shade can block all or part of the night sky.
Retractable awnings are known. Such awnings are conventionally mounted to a vertical structure, such as the wall of a house or commercial premises, and can be extended and retracted by actuation of a gear train which extends and retracts articulating arms that support the awning fabric. The arms typically have a central pivot point, and bend as the awning is retracted to draw the fabric toward the structure; or alternatively unfold as the awning is extended, unfurling the awning fabric and stretching it taut. However, such awnings are typically supported only on one end, and unless the other end is supported by cables or the like from a significantly higher point (which is not always possible), they can practically extend only few meters from the structure before the weight of the extended awning applies too much torque to the mounting point to safely support the awning. Also, when such an awning is extended it can only be retracted by actuation of the gear train, and therefore a high wind catching the awning in the wrong direction can damage the frame or tear the awning away from the structure.
In awnings that are supported on a frame along their depth, the booms are driven at both ends. This leads to frequent jamming, since the ends cannot always be driven at exactly the same rate, especially where a wood supporting frame is used because the shape of the frame and in particular the alignment between joists changes over time.